High density microwell plates or micro-reactors have been fabricated using various methods to form an array of sites or wells within a single surface. Although densities have become high, they are often limited by pattern formation and manufacturing techniques with often limited well height to width aspect ratios on only a single planar surface. As a result, a large usable area between the microwells is lost depending on the pitch or spacing between adjacent wells. As the footprint of the microwell size is reduced to accommodate even higher densities, the ratio of usable microwell area to dead space decreases exponentially resulting in even greater loss of usable area on the imaging plane for high density microwell reactors. The density loss due to well spacing must be minimized or eliminated to achieve higher densities.
In addition, limits in the manufacturability of high aspect ratio microwells makes it prohibitive to increase reactor densities beyond a certain value as it begins to adversely affect the possible reactor volumes or imaging resolution. Also, it is prohibitively difficult to fill each microwell reactor as the aspect ratio increases due to the dominant effects of surface tension at such small length scales. This prohibits fluid from reliably filling each reactor well completely.
More recently, attempts have been made to increase density and area coverage efficiency by using three-dimensional droplet emulsion arrays. For example, U.S. Patent Application Publication No. 2012-0184464 describes a system and method for the high density assembly and packing of micro-reactors. This method increases density and area coverage efficiency, however droplets are prone to movement over time, and require high surfactant concentrations to prevent droplet coalescence.